Anisotropic magnetoresistance (AMR) sensors have replaced classical magneto-inductive coils in hard-drive read heads launching the era of spintronics. Their utility has, however, remained limited partly because the response of these ferromagnetic resistors to changes in magnetization orientation originates from generically subtle spin-orbit (SO) interaction effects.
Currently, giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) elements are used having at least two magnetically decoupled ferromagnetic layers which provide a remarkably elegant way of tying the magnetoresistance response directly to the ferromagnetic exchange splitting of the carrier bands without involving SO-coupling. Large magnetoresistances in these types of devices are usually obtained at the expense of a significantly increased structure complexity, to provide independent and different magnetization switching characteristics and spin-coherence of transport between the ferromagnetic layers.
Studies of AMR effects in ferromagnetic semiconductor tunneling devices show that AMR response can, in principle, be huge and richer than TMR, with the magnitude and sign of the magnetoresistance dependent on the magnetic field orientation and electric fields. Reference is made to “Tunneling Anisotropic Magnetoresistance: A Spin-Valve-Like Tunnel Magnetoresistance Using a Single Magnetic Layer” by C. Gould et al., Physical Review Letters, volume 93, page 117203 (2004) and “Very Large Tunneling Anisotropic Magnetoresistance of a (Ga,Mn)As/GaAs/(Ga,Mn)As Stack” by C. Rüster, C. Gould, T. Jungwirth, J. Sinova, G. M. Schott, R. Giraud, K. Brunner, G. Schmidt, and L. W. Molenkamp, Physical Review Letters, volume 94, page 027203 (2005).
Experimental demonstration of tunneling anisotropic magnetoresistance (TAMR) in a tunnel junction with a ferromagnetic metal electrode has recently been reported for an epitaxial Fe/GaAs/Au stack and reference is made to “Tunneling Anisotropic Magnetoresistance and Spin-Orbit Coupling in Fe/GaAs/Au Tunnel Junctions” by J. Moser, A. Matos-Abiague, D. Schuh, W. Wegscheider, J. Fabian, and D. Weiss, Physical Review Letters, volume 99, page 056601 (2007). The observed TAMR in this structure is relatively small, bellow 0.5%, consistent with the weak SO-coupling in Fe.
The present invention seeks to provide an improved magnetoresistive device.